The present invention relates to wrist prostheses, and especially to prosthesis for a total wrist arthroplasty. More specifically, the invention concerns a modular prosthesis that permits modification in a revision surgery.
In a total wrist arthroplasty, radial and metacarpal components are engaged to the radius and metacarpal bones, respectively. In a common wrist prosthesis, the radial and metacarpal components define an articulating interface that emulates the natural movement of the patient's wrist. In more recent total wrist prostheses, the articulating interface is defined by ellipsoidal joint elements that eliminate problematic axial rotation and limit the articulation along the axes for flexion/extension and radial/ulnar deflection.
As wrist prostheses have evolved, the trend has been toward modularity. This modularity allows a wrist prosthesis to be specifically tailored to a patient's anatomy. Consequently, some prosthesis offer differently sized radial and metacarpal components. For instance, in some implants, as represented by U.S. Pat. No. 6,485,520, different articulating elements can be selected, with the selected elements being fastened together with machine screws. Thus, in these prior implants, the benefit of modularity is appreciated only when the prosthesis is initially constructed. These implants cannot be modified in a revision surgery without completely removing the affected arthroplasty component.
Until the last decade, total wrist arthroplasty (TWA) was a rarely used option over wrist fusion because of the difficulty in obtaining long-term fixation of the metacarpal/distal side. Improvements in the design of the metacarpal component have led to increasing favor for TWA. In the typical TWA prosthesis, the modularity is restricted to the metacarpal component. One problem with this approach is that the profile height of the metacarpal component must be prominent in order to accept the modular components. This increased height increases the lever arm force exerted on the prosthetic joint. This increased force manifests itself in undesirable loosening of the metacarpal fixation, which can require an invasive revision surgery to remove or repair the loosened metacarpal component.
There is a need in the field of total wrist arthroplasty for a modular system that does not suffer from the difficulties commonly associated with current TWA. There is a further need for a modular system in which the benefits of modularity can be capitalized on in a minimally invasive revision surgery or procedure to restore proper joint tension and spacing of the joint components.